Lots of people have been asking me to unlock their phones but I don’t offer this service. I posted about unlocking mobile phones because I was very happy when O2 supplied us with the unlock codes for all the mobiles phones we had in the house for free just by asking them. Before this I had the wrong idea that I should pay somebody for the unlocking service when most network providers give the unlock code free of charge. So, to clarify the situation I am telling you how I got my mobile phones unlocked for free.
Firstly I read about mobile phone unlocking in the O2 web site help session:

“Q. My phone is locked to the O2 network. How do I unlock it?
A. Please call Customer Care if you would like your phone unlocked.
Some things to note before you call us; O2 Speak easy customers must have topped up a minimum of 150 EURO in total before we can unlock the phone. Exceptions to this are if you are porting to another network or if you are roaming in another country with which O2 has no agreement.
You will need to have the following information to hand when you call Customer Care as this is required to obtain the unlock code :
your IMEI serial number To get your 15-digit IMEI dial *#06# and it will appear on the screen or it should be noted on a sticker on the device underneath the battery.
the make and model of your phone e.g., Nokia 6230i
In some cases we will need to contact the manufacturer of your phone for the unlock code, this will take extra time but we will advise you of the approximate wait time.”

Instead of calling the Customer Care I sent them an e-mail asking for the unlocking codes. In the e-mail I explained that I was travelling to South America and to avoid problems I needed to unlock my mobile phone to be able to use any SIM card as there are some countries e.g. Venezuela where O2 does not have roaming agreement with.
In the e-mail I informed:

• My mobile phone brand and model.
• The 15-digit IMEI which can be seen when you dial *#06#
• My mobile phone number
• My name

I also asked for instructions on how to input the codes in order to have the mobile phone unlocked.
O2 answered promptly and sent me the unlocking codes and the procedures by e-mail.
You can contact O2 using the “Contact Query form” they have in their website, in this form there is a field called “I want to” where you can choose the “unlock my mobile” option.
The link to the “Contact Query form” is: http://www.o2online.ie/wps/wcm/connect/O2/Home/Help+and+Support/Contact+Us/Contact+Query+form
I hope this information is useful for you.